function 全部() {
    x = document.getElementById("C1"); // 找到元素
    x.innerHTML = "空空如也";           // 改变内容
    y = document.getElementById("C2");
    y.innerHTML = "我也空空如也";
    //z = document.getElementById("1");     //命名函数
    //z.style.color = "#00AEEC";           // 改变样式
}
function 视频投稿() {
    x = document.getElementById("C1");
    x.innerHTML = "没东西";
    y = document.getElementById("C2");
    y.innerHTML = "偶吼吼";

}
function 追番追剧() {
    x = document.getElementById("C1");
    x.innerHTML = "你还在看什么？";
    y = document.getElementById("C2");
    y.innerHTML = "一个子也没有啦";

}
function 专栏() {
    x = document.getElementById("C1");
    x.innerHTML = "哇塞";
    y = document.getElementById("C2");
    y.innerHTML = "真锲而不舍";
}
const back_top = document.querySelector("#back_top")
window.addEventListener("scroll", function () {
    const n = document.documentElement.scrollTop
    back_top.style.opacity = n >= 600 ? 1 : 0
})
back_top.addEventListener("click", function () {
    document.documentElement.scrollTop = 0
})
